1. Field of the Invention
The present invention relates generally to a printed circuit board and a semiconductor chip package with the same, and more particularly, to a printed circuit board having a structure for relieving a stress concentration on corner leads that are connected to a semiconductor device on the printed circuit board, and a semiconductor chip package equipped with the same printed circuit board.
2. Description of the Related Art
FIG. 1 is a top view of a flexible printed circuit board 1 connected to a display module of a liquid crystal display device, as an example of a printed circuit board on which a semiconductor device is mounted.
Referring to FIG. 1, an external connection terminal 3 to be connected to the display module of the liquid crystal display device is located in one side of the flexible printed circuit board 1, another external connection terminal 4 to be connected to a control panel allowing a user to control the liquid crystal display device is located in the other side of the flexible printed circuit board 1, and an inner lead portion 2 to be connected to a semiconductor device for driving is formed in a predetermined portion of the flexible printed circuit board 1. The semiconductor device for driving drives the liquid crystal display module according to a signal received from the control panel. An electrical and mechanical connection between the flexible printed circuit board 1 and the semiconductor device is achieved by connections between leads located in the inner lead portion 2 of the flexible printed circuit board 1 and bumps formed on the semiconductor device.
FIG. 2 is an enlarged view of the inner lead portion 2 on the flexible printed circuit board shown in FIG. 1.
Referring to FIG. 2, the inner lead portion 2 includes a plurality of leads 21 and 24. The leads 21 and 24 are arranged around a rectangular area on which a semiconductor device 5 will be mounted. That is, the leads 21 and 24 are perpendicular, respectively, to the four sides of the semiconductor device 5 with a rectangle shape.
Each of the leads 21 and 24, arranged as described above, is connected one-to-one with a bump 51 formed on the semiconductor device 5, thereby electrically and mechanically connecting the flexible printed circuit board 1 to the semiconductor device 5.
The one-to-one connection of the bump 51 and each of the leads 21 and 24 is achieved by Au—Sn eutectic bonding at a high temperature. However, a peel stress is concentrated on leads located near the corners of the semiconductor device 5, due to loads caused by a difference in thermal expansion coefficients between the flexible printed circuit board 1 and the semiconductor device 5 while the one-to-one connections are formed and cooled. Such concentration of the peel stress results in breakage of the leads. Accordingly, a solution for avoiding such breakage is needed.
FIG. 3 is an enlarged view of a portion III of FIG. 2.
Referring to FIG. 3, conventionally, to relieve the stress concentration due to the difference in the thermal expansion coefficients and to prevent the breakage of the leads located near the corners of the semiconductor device 5, dummy leads 23 are formed near the edges of the longitudinal sides of the semiconductor device 5 and each of the dummy leads 23 is connected to a bump 51 on the semiconductor device 5. Therefore, the peel stress is concentrated on the dummy leads 23, thereby preventing the leads 21 through which signals are passed from being damaged.
However, in the conventional method in which the dummy leads 23 are formed, there is no design rule for the width (W) and length of a dummy lead, a distance (G1) between the dummy lead and a lead adjacent to the dummy lead, etc. In particular, if a pitch of a lead is smaller than 30 μm, a structure and design for relieving the stress concentration on the corner leads 21 using a quantified method is required.